U.S. patent number 5,234,866 [Application Number 07/863,060] was granted by the patent office on 1993-08-10 for semiconductor device and process for producing the same, and lead frame used in said process.
This patent grant is currently assigned to Hitachi, Ltd., Hitachi VLSI Engineering Corp.. Invention is credited to Michiaki Furukawa, Takayuki Okinaga, Kanji Otsuka, Hiroshi Ozaki, Hiroshi Tachi, Yasuyuki Yamasaki.
United States Patent |
5,234,866 |
Okinaga , et al. |
August 10, 1993 |
Semiconductor device and process for producing the same, and lead
frame used in said process
Abstract
According to the present invention, as improvement in the
adhesion of inner leads with a packaging resin in a resin-sealed
semiconductor device is attained by spreading leads on or near the
circuit-forming face of a pellet, or on or near the main
non-circuit-forming face of the pellet to extend the lengths of the
inner leads on or under the pellet.
Inventors: |
Okinaga; Takayuki (Akishima,
JP), Tachi; Hiroshi (Akishima, JP), Ozaki;
Hiroshi (Kokubunji, JP), Otsuka; Kanji
(Higashiyamato, JP), Furukawa; Michiaki (Mizuho,
JP), Yamasaki; Yasuyuki (Kokubunji, JP) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JP)
Hitachi VLSI Engineering Corp. (Tokyo, JP)
|
Family
ID: |
26399465 |
Appl.
No.: |
07/863,060 |
Filed: |
April 3, 1992 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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529448 |
May 29, 1990 |
5126821 |
|
|
|
445942 |
Dec 18, 1989 |
4943843 |
|
|
|
240605 |
Sep 6, 1988 |
|
|
|
|
845332 |
Mar 21, 1986 |
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Foreign Application Priority Data
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Mar 25, 1985 [JP] |
|
|
60-58407 |
|
Current U.S.
Class: |
29/827;
257/E23.066; 438/118; 257/E23.039; 257/E21.505; 257/E23.049;
257/E23.056 |
Current CPC
Class: |
H01L
24/83 (20130101); H01L 23/49558 (20130101); H01L
23/49861 (20130101); H01L 23/4951 (20130101); H01L
24/32 (20130101); H01L 23/49586 (20130101); H01L
2224/48465 (20130101); H01L 2924/01082 (20130101); H01L
2224/83051 (20130101); H01L 2924/01027 (20130101); H01L
2924/07802 (20130101); H01L 2224/45144 (20130101); H01L
24/45 (20130101); Y10T 29/49121 (20150115); H01L
2924/14 (20130101); H01L 2224/2919 (20130101); H01L
2224/48091 (20130101); H01L 2224/48247 (20130101); H01L
2224/05554 (20130101); H01L 2224/4826 (20130101); H01L
24/48 (20130101); H01L 2224/8385 (20130101); H01L
2224/8319 (20130101); H01L 2924/01079 (20130101); H01L
2224/97 (20130101); H01L 2924/01033 (20130101); H01L
2924/01078 (20130101); H01L 2224/73215 (20130101); H01L
2224/48227 (20130101); H01L 2924/0132 (20130101); H01L
2924/00014 (20130101); H01L 2924/0665 (20130101); H01L
2924/181 (20130101); H01L 2924/01023 (20130101); H01L
2224/27013 (20130101); H01L 2224/451 (20130101); H01L
2224/32245 (20130101); H01L 2224/73265 (20130101); H01L
2224/48091 (20130101); H01L 2924/00014 (20130101); H01L
2224/97 (20130101); H01L 2224/85 (20130101); H01L
2224/97 (20130101); H01L 2224/83 (20130101); H01L
2224/73265 (20130101); H01L 2224/32245 (20130101); H01L
2224/48247 (20130101); H01L 2224/2919 (20130101); H01L
2924/0665 (20130101); H01L 2924/00 (20130101); H01L
2924/0665 (20130101); H01L 2924/00 (20130101); H01L
2224/48465 (20130101); H01L 2224/48227 (20130101); H01L
2224/48465 (20130101); H01L 2224/48227 (20130101); H01L
2924/00 (20130101); H01L 2224/48465 (20130101); H01L
2224/48247 (20130101); H01L 2924/00 (20130101); H01L
2924/0132 (20130101); H01L 2924/01006 (20130101); H01L
2924/01014 (20130101); H01L 2224/48465 (20130101); H01L
2224/48091 (20130101); H01L 2924/00 (20130101); H01L
2224/73265 (20130101); H01L 2224/32245 (20130101); H01L
2224/48227 (20130101); H01L 2924/00 (20130101); H01L
2224/451 (20130101); H01L 2924/00015 (20130101); H01L
2224/45144 (20130101); H01L 2924/00014 (20130101); H01L
2924/00014 (20130101); H01L 2224/05599 (20130101); H01L
2924/181 (20130101); H01L 2924/00012 (20130101); H01L
2224/73215 (20130101); H01L 2224/32245 (20130101); H01L
2224/4826 (20130101); H01L 2924/00 (20130101); H01L
2224/48465 (20130101); H01L 2224/4826 (20130101); H01L
2924/00 (20130101) |
Current International
Class: |
H01L
23/498 (20060101); H01L 21/02 (20060101); H01L
21/58 (20060101); H01L 23/48 (20060101); H01L
23/495 (20060101); H01L 021/60 () |
Field of
Search: |
;437/209,211,215,217
;357/70,74,80 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hearn; Brian E.
Assistant Examiner: Picardat; Kevin M.
Attorney, Agent or Firm: Antonelli, Terry, Stout &
Kraus
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a divisional of application Ser. No. 529,448,
filed May 29, 1990 (now U.S. Pat. No. 5,126,821), which is a
divisional of application Ser. No. 445,942, filed Dec. 8, 1989 (now
U.S. Pat. No. 4,943,843), which is a continuation of application
Ser. No. 240,605, filed Sep. 6, 1988 (now abandoned), which is a
continuation of application Ser. No. 845,332, filed Mar. 21, 1986
(now abandoned).
Claims
What is claimed is:
1. A method of producing a semiconductor device comprising the
steps of:
preparing a lead frame having a plurality of leads each including a
first end and a pellet having a circuit-forming face with a
plurality of bonding pads on said circuit-forming face;
bonding said plurality of leads at said first end to an insulating
sheet;
after bonding said plurality of leads to said insulating sheet,
bonding said insulating sheet to said circuit-forming face via an
adhesive;
electrically connecting one of said plurality of leads at said
first end to one of said bonding pads; and
molding said pellet and plurality of said leads with a resin.
2. A method of producing a semiconductor device according to claim
1, wherein said insulating sheet comprises a polyimide resin.
3. A method of producing a semiconductor device according to claim
1, wherein said one of said plurality of leads are connected to
said one of bonding pads by a bonding wire.
4. A method of producing a semiconductor device according to claim
3, wherein said resin comprises epoxy resin.
5. A method of producing a semiconductor device according to claim
1, wherein said insulating sheet is bonded to said circuit-forming
face at a position except bonding pads.
6. A method of producing a semiconductor device comprising the
steps of:
preparing a lead frame having a plurality of leads each including a
first end with an insulating sheet attached to said first ends of
said plurality of leads, and a pellet having a circuit-forming face
with a plurality of bonding pads on said circuit-forming face;
bonding said insulating sheet to said circuit-forming face via an
adhesive;
electrically connecting one of said plurality of leads at said
first end to one of said bonding pads; and
molding said pad and plurality of said leads with a resin.
7. A method of producing a semiconductor device according to claim
6, wherein said insulating sheet comprises a polyimide resin.
8. A method of producing a semiconductor device according to claim
6, wherein said one of said plurality of leads are connected to
said one of bonding pads by a bonding wire.
9. A method of producing a semiconductor device according to claim
6, wherein said resin comprises epoxy resin.
10. A method of producing a semiconductor device according to claim
6, wherein said insulating sheet is bonded to said circuit-forming
face at a portion except bonding pads.
11. A method of producing a semiconductor device comprising the
steps of:
preparing a lead frame having a plurality of leads each including a
first end with an insulating sheet attached to said first ends of
said plurality of leads, and a pellet having a circuit-forming face
with a plurality of bonding pads on said circuit-forming face and a
non-circuit-forming face;
bonding said insulating sheet to said non-circuit-forming face via
an adhesive;
electrically connecting one of said plurality of leads to one of
said bonding pads; and
molding said pellet and plurality of said leads with a resin.
12. A method of producing a semiconductor device according to claim
11, wherein said insulating sheet comprises a polyimide resin.
13. A method of producing a semiconductor device according to claim
11, wherein said one of said plurality of leads are connected to
said one of bonding pads by a bonding wire.
14. A method of producing a semiconductor device according to claim
11, wherein said resin comprises epoxy resin.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a technique that is especially
applicable for providing an electrical connection to a pellet in a
resin-sealed semiconductor device.
FIG. 8 is a plan view of a conventional lead frame, which is used
in the production of a conventional resin-sealed semiconductor
device, specifically a resin-sealed type of 64 KSRAM (memory) LSI.
In the figure, the numeral 100 indicates a frame, 101 an outer
frame, 102 an inner lead, 103 a tie bar, 104 a tab, and 105 a tab
lead.
In the resin-sealed semiconductor device, there is a tendency that
the distance between the side end of a package and the tab, which
is a pellet mounting part, becomes increasingly narrower with a
trend of the pellet size being increased. This is attributed to the
fact that the size of a package for pellets is standardized and,
hence, cannot be enlarged despite the increasing size of the
pellet.
As a result, it is anticipated that, since this may entail largely
lowered adhesion of so-called short leads which are structurally
short lengths of the portions of the leads as external terminals
where the leads are embedded within a resin constituting the
package, the leads are liable to easily fall off and peeling is
liable to occur between the leads and the resin during bending work
of the lead.
The inventors of the present invention have found that this may
lead to poor electrical connection, reduction in moisture
resistance, etc., to reduce the reliability of the semiconductor
device.
Resin-sealed semiconductor devices are described in "IC-Ka Jisso
Gijutsu", pp. 149-150, edited by Nihon Microelectronics Society and
published by Kogyo Chosakai Publishing Co., Ltd. on Jan. 15,
1980.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a technique which
serves to remarkably improve the adhesion of a resin of a package
with the leads in a resin-sealed semiconductor device, especially
in a semiconductor device on which a large semiconductor pellet is
mounted.
The aforementioned and other objects and novel features of the
invention will become apparent from the following description and
the accompanying drawings.
An outline of a representative embodiment of the invention will now
be briefly described.
Specifically, an improvement in adhesion between inner portions of
the leads and a resin constituting a package is achieved by
spreading a lead on or near the circuit-forming face of a pellet to
be mounted, or on or near the main non-circuit-forming face of the
pellet in a resin-sealed semiconductor device to enable the inner
portion of the lead; i.e., the portion embedded in the resin, to be
elongated and thereby provide a greater contact area with the
resin.
BRIEF DESCRIPTION OF THE DRAWINGS
The aforementioned and other objects and novel features of the
present invention will become apparent from the following
description taken with reference to the accompanying drawings in
which:
FIG. 1 is a cross-sectional view taken along line I--I in FIG. 2
showing a semiconductor device of Example 1 according to the
present invention;
FIG. 2 is a plan view showing the relation of a pellet and the
leads of the semiconductor device of Example 1;
FIG. 3 is a partial plan view of a lead frame used in the
semiconductor device of Example 1, and shows a state of the frame
in the step of plating;
FIG. 4 is a plan view showing the relation of a pellet and the
leads of a semiconductor device of Example 2 according to the
present invention;
FIG. 5 is a partial cross-sectional view taken along line V--V in
FIG. 4 showing the internal structure of the semiconductor device
of Example 2;
FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. 7
showing a semiconductor device of Example 3 according to the
present invention;
FIG. 7 is a plan view showing the relation of a pellet and leads of
the semiconductor device of Example 3; and
FIG. 8 is a plan view of a lead frame used in the production of a
conventional resin-sealed semiconductor device.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Example 1
FIG. 1 is a cross-sectional view taken along line I-I in FIG. 2
showing a semiconductor device of Example 1 according to the
present invention. FIG. 2 is a plan view showing the relation of a
pellet and the leads of the semiconductor device of Example 1.
The semiconductor device of Example 1 is a so-called resin-sealed
semiconductor device. Specifically, the semiconductor pellet 1 is
embedded together with the inner portions of the leads 2, which
portions of the leads 2 serve as external terminals in a resin 4
constituting a package 3, such as an epoxy resin (hereinafter
referred to as "packaging resin"), and the outer portions of the
leads 2 outside the package are bended downward near the side ends
of the package 3.
In a conventional resin-sealed semiconductor device, a pellet is
attached to a tab, which serves as a mounting board having
substantially the same size as that of the pellet, and bonding
pads, which serve as the electrodes of the pellet, are electrically
connected with the inner end portions of the leads disposed at the
periphery of the tab via fine metallic wires which serve as bonding
wires.
By contrast, in the semiconductor device of Example 1, the leads
are spread (i.e., arranged to extend in an elongated manner) on the
reverse side of the pellet 1 (namely, the main non-circuit-forming
face on which no semiconductor integrated circuit is formed). The
pellet is attached via an adhesive 6 to an insulating sheet 5 of a
polyimide resin bonded to the leads. In this case, the lead frame
has no tab which serves as the pellet mounting part. The insulating
sheet 5 serves to provide electrical insulation between the leads.
In this Example, if there were no insulating sheet 5, an electrical
short circuit would be produced between the leads by the conductive
pellet 1. In order to avoid the electrical short circuit, the
insulating sheet 5 is disposed between the pellet 1 and the
leads.
As shown in FIG. 2, the positional relation of the above-mentioned
pellet 1 and the leads 2 is such that the inner portions of the
leads 2a whose outer portions are disposed along the sides of the
pellet 1 near which no bonding pads 7 are formed in the arrangement
(hereinafter referred to also as "non-bonding pad-forming sides")
are spread on the reverse side (main non-circuit-forming face) of
the pellet 1, and that the tip portions 2b of the leads are spread
up to the positions exceeding the sides of the pellet near which
bonding pads 7 are formed in the arrangement. The insulating sheet
5 is bonded onto the leads 2a, and the pellet 1 is attached on the
upper face of the insulating sheet 5 with the main
non-circuit-forming face disposed on the lower side.
In the conventional resin-sealed semiconductor devices, the
position where the leads, corresponding to the leads 2a of the
invention having the inner lead portions spread under the pellet 1,
are embedded in the packaging resin is the region of the packaging
resin where the inner lead portions (those portions of the leads
which are embedded in the packaging resin) can merely secure an
extremely limited short length ranging from the side end of the
package to the proximity of the tab; namely, the place where the
short leads are provided.
The conventional short leads usually cause a problem in that they
are liable to fall off from the package because of low tensile
strength attributed to small bonding areas thereof shared with the
package resin. Since the bonding areas shared by the short leads
and the packaging resin are reduced with an increasing size of the
pellet, this problem has become serious with an increase in the
pellet size.
By contrast, since the inner portions of the leads 2a provided in
the places corresponding to the positions of the above-mentioned
short leads are very long; i.e., these portions are elongated, in
the semiconductor device of Example 1, the bonding areas thereof
shared with the packaging resin are large. Thus, the bonding
strength between the leads and the packaging resin can be largely
improved. Therefore, peeling in the interface between the leads and
the packaging resin which may occur in bending work of the outer
portions of the leads or the like can be effectively prevented even
in a semiconductor device in which a large pellet is used, thus
avoiding intrusion of water up to the pellet in the packaging resin
through the peeled portion from the outside. Thus, the moisture
resistance of the semiconductor device can be improved.
Furthermore, since the insulating sheet 5 is strongly bonded to the
leads 2a, the latter have a very high tensile strength.
Moreover, since the leads 2a, formed of a metallic material having
higher heat conductivity and heat dissipating ability than the
packaging resin, are attached to the pellet 1 over a wide range of
the face thereof though the attachment made via the insulating
sheet 5, the heat generated in the pellet in an operating state can
be directly dissipated toward the outside via the leads. Thus, the
semiconductor device of the present invention is one having a
structure with an excellent heat dissipating ability.
Besides, since the electrical connection of the pellet 1 with the
leads 2a is achieved by wire-bonding the bonding pad 7a in the
pellet 1 with the tip portions 2b of the leads 2a spread near them
and near the sides of the pellet, the bonding wires 8 can be
shortened. Therefore, a contact accident between mutually adjacent
bonding wires, between a bonding wire and an adjacent lead, or
between a bonding wire and the pellet can be prevented. In other
words, occurrence of a short circuit accident can be prevented.
Further, the amount of the wires 8 can be decreased due to the
small length of the bonding wires, thus attaining cost
reduction.
The semiconductor device of Example 1 is easily prepared by forming
a lead frame for predetermined shapes of leads, bonding an
insulating sheet 5 in the predetermined portions of the inner
portions of the leads, attaching a pellet 1 to the insulating sheet
5 via an adhesive, effecting wire-bonding of the bonding pads 7 of
the pellet 1 with the bonding parts of the leads, and following the
same assembly step as in the case of the conventional resin-sealed
semiconductor device. In this case, the insulating sheet 5 not only
serves as an insulator for preventing a short circuit accident
between the leads, but also plays a role of reinforcing the lead
frame in respect of the mechanical strength thereof.
The wire-bonding parts of the above-mentioned leads can be formed
by depositing gold according to, for example, the partial plating
method.
FIG. 3 is a partial plan view of the lead frame having the
insulating sheet 5 bonded thereto in the portion thereof
substantially inside the tie bar 9. The lead frame portions not
shown in the figure, for example, the frame portion and the outer
lead portion, have shapes similar to those of a lead frame shown in
FIG. 8. In the semiconductor device of Example 1, since the
insulating sheet 5 itself functions as a partial plating mask, use
of only a partial plating mask having an opening as shown by the
dot mark domain in FIG. 3 makes it possible to effect selective
partial plating of a material having excellent wire bonding
ability, such as gold (Au), in only the tip portions 2b of the
leads 2. Therefore, in the case of effecting partial plating, the
mask preparation process is simplified, thus enabling easy
formation of the bonding parts.
In FIG. 3 a mask providing spaces only along the short sides of the
pellet is shown. However, use of a mask having an opening also
providing spaces along the long sides of the pellet parallel to the
tie bars 9 makes it possible to easily effect partial plating on
the leads all around the insulating sheet 5. In this way, a
semiconductor device having pellet whose periphery is provided all
along with bonding pads can be easily prepared.
Example 2
FIG. 4 is a plan view showing the relation of a pellet and leads of
a semiconductor device of another Example according to the present
invention.
The semiconductor device of Example 2 is different from that of
Example 1 in that no insulating sheet 5 is used and that a smaller
tab than the pellet 1 is used.
Specifically, in the semiconductor device of Example 2, the pellet
1 is attached, via an adhesive 11 of an insulating material, to the
tab and the inner portions 2b of leads 2a whose outer portions are
arranged along the non-bonding pad-forming sides of the pellet.
Usable adhesives of insulating materials include polyimide resins,
silicone rubbers, and ceramics.
In Example 2, since there is no insulating sheet 5, heat can be
directly dissipated from the pellet 1. Thus the heat resistance is
further lowered as compared with that in Example 1 and, hence, the
reliability is correspondingly higher.
Furthermore, since the tab 10 is attached, the pellet attachment
strength is also secured.
FIG. 5 is a partial cross-sectional view showing the state of
electrical connection of the pellet 1 with the tip portions of the
leads 2 in the view taken along line V--V in FIG. 4. A recess 2c is
formed in the tip portion 2b of a lead 2a. In bonding of the pellet
1 with the adhesive 11, since the adhesive 11 may flow out to
contaminate the surface of the bonding part 12, bonding of the
bonding pad 7 of the pellet 1 and the bonding part 12 with a wire 8
cannot sometimes be effected. The above-mentioned recess 2c is
provided as a dam serving to intercept the flow of the adhesive 11
for avoiding the occurrence of failure of the bonding.
Example 3
FIG. 6 is a cross-sectional view of a semiconductor device of still
another Example according to the present invention. FIG. 7 is a
plan view showing the relation of a pellet and leads in the
above-mentioned semiconductor device.
The semiconductor device of Example 3 is different from those of
Examples 1 and 2 in that the inner portions of the leads are spread
on the circuit-forming face of the pellet.
Specifically, as shown in FIG. 6, the pellet 1 is attached, via an
adhesive 6, onto the circuit-forming face of the pellet via an
insulating sheet 5 of a polyimide resin bonded onto the reverse
face of the inner portions of the leads. In this case, the
insulating sheet 5 functions as an insulator for preventing a short
circuit accident between the leads. Besides, the insulating sheet 5
plays a role of reinforcing the leads in respect of the mechanical
strength thereof.
As shown in FIG. 7, the insulating sheet 5 has such a size that it
does not cover the bonding pads of the pellet 1 bonded thereto. The
inner portions of the leads 2a having outer portions arranged along
the non-bonding pad-forming sides of the pellet are spread on the
upper face of the insulating sheet. The inner portions of the leads
2a are bonded to the above-mentioned insulating sheet 5a with the
tip portions thereof positioned short of the bonding pads.
Since the semiconductor device of Example 3 has the inner portions
of the leads bonded on the side of the circuit-forming face of the
pellet 1, it is superior in heat dissipating ability to the device
of Example 1.
The polyimide resin of the insulating sheet 5 serves to prevent a
semiconductor element from malfunctioning when the semiconductor
device is irradiated with .alpha. rays from outside. Namely, the
insulating sheet 5 plays a role of blocking the .alpha. rays
intruding the device from outside to intercept irradiation of the
semiconductor element with the .alpha. rays. Since the insulating
sheet covers the circuit-forming face, an improvement in
reliability against .alpha. rays is attained, too.
In a semiconductor device having an insulating film applied as the
passivation film protecting the electric wiring and circuit
portions on the circuit-forming face of the pellet 1, the
insulating sheet for preventing short circuit between the leads may
be unnecessary, or not only an insulating material but also a
conductive material can be used as the adhesive for bonding the
pellet to the leads and, if necessary, to the tab.
In Example 3, the tip portions 2b of the leads 2a are disposed in
the inner positions short of the bonding pads 7, the positional
relation therebetween is inversed in comparison with that in
Example 1. Thus, the bonding direction is inversed, too. However,
the bonding distance is substantially the same as in Example 1.
The effects of the present invention are as follows.
(1) In the resin-sealed semiconductor device, the spread of inner
portions of leads on or near the circuit-forming face of a pellet
mounted in the device, or on or near the main non-circuit-forming
face of the pellet can greatly improve the adhesion of the inner
portions of the leads with the packaging resin. Therefore, even
where a large pellet is mounted, the leads can be prevented from
falling off from the packaging resin.
In the present invention, at least one of the inner portions of the
leads is spread on or under the pellet. As a result, the adhesion
of the inner portions with the packaging resin can be greatly
improved. Therefore, even where a large pellet is mounted, leads
can be prevented from falling off from the packaging resin.
(2) For the same reason as mentioned in (1) above, occurrence of
peeling in the bonding face between the leads and the packaging
resin can be prevented in the bending work of the outer portions of
the leads.
(3) For the reasons as mentioned in (1) and (2) above, even in the
case of a semiconductor device having a small package and a large
pellet mounted therein, there can be provided a highly reliable
semiconductor device excellent in moisture resistance.
(4) When the inner portions of the leads are attached onto the main
non-circuit-forming face of the pellet, heat generated in an
operating state can be effectively dissipated through the leads
toward outside.
(5) When an insulating sheet is provided between the pellet and the
inner leads in the device as mentioned in (4) above, the attachment
strength of the pellet can be improved.
(6) The structure as mentioned in (5) above can be easily formed by
preparing a lead frame having an insulating sheet bonded thereto in
a predetermined portion thereof and attaching a pellet onto the
insulating sheet.
(7) Since the leads can be reinforced by bonding the insulating
sheet to the lead frame in the predetermined portion thereof, the
lead frame can be easily handled even if it includes a large number
of fine leads.
(8) A combination of the lead frame having the insulating sheet
bonded thereto in the predetermined portion thereof and a partial
plating mask having an opening with a size providing a space(s) all
or partially around the insulating sheet enables the portions of
the leads corresponding to the above-mentioned space(s) to be
easily subjected to partial plating since the insulating sheet
functions as a mask of partial plating, too.
(9) Attachment of the inner portions of the leads onto the
circuit-forming face of the pellet enables heat generated in the
circuit in an operating state to be more directly dissipated
through the leads.
(10) Provision of the insulating sheet, which serves to intercept
irradiation of semiconductor elements with .alpha. rays between the
inner leads and the pellet, can protect the semiconductor elements
and a circuit including the same from the .alpha. rays. Thus the
reliability of the semiconductor device against .alpha. rays can be
improved.
(11) When the leads attached onto the circuit-forming face or
non-circuit-forming face of the pellet are provided with recesses
or protrusions in the positions thereof close to the pellet
mounting parts thereof, an adhesive for bonding them to the pellet
or the insulating sheet for attachment of the pellet thereto can be
prevented from flowing out to contaminate the surfaces of the
bonding parts. Thus occurrence of poor wire-bonding can be
prevented.
The invention completed by the present inventors has been
specifically described with reference to Examples. However, the
present invention is not limited to the above-mentioned Examples
and is, needless to say, capable of various modifications within a
range where they are not deviated from the subject matter of the
present invention.
For example, all Examples concern the case where the inner portions
of the leads are directly or indirectly attached onto the main face
of the pellet. However, the present invention is not limited to
this case. All or part of the inner portions of the leads may be
spread near the circuit-forming face or the main
non-circuit-forming face. Moreover, although the inner portions of
the leads are shown spread along an arcuate or angled path with
linear sections being joined together, the inner portions of the
leads may also be formed as continuous curved sections.
Also, all Examples concern the case where only the leads on the
sides of the pellet corresponding to the positions of the so-called
short leads are spread. However, the present invention is not
limited to this case, and includes a case where leads having long
inner portions are spread in a usual semiconductor device. The
insulating sheet is not limited to one of a polyimide resin, and
may be one of a silicon rubber. A heat-conductive filler such as a
silicon carbide powder (SiC) may, of course, be incorporated into
the adhesive and/or the insulating sheet in order to improve the
heat dissipating ability.
In Examples 1 and 3, the insulating sheet may not necessarily be
used. In contrast, in Example 2, an insulating sheet may be
used.
The dam for preventing the adhesive of the leads from flowing out
as revealed in Example 2 is not limited to a recess, but may be a
protrusion. This kind of dam may, of course, be employed in
Examples 1 and 2.
The foregoing description mainly concerns the case where the
invention completed by the present inventors is applied to the
so-called DIP (Duel In-Line Plastic) type semiconductor device
concerned with the application field as the background of the
present invention. However, the present invention is not limited to
this type of device. The technique of the present invention can be
effectively applied to semiconductor devices with various forms of
package structures such as a flat package structure in so far as
the package is formed by sealing with a resin.
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